Many cake recipes ask to add melted butter and mix it in. In my experience butter needs to be melted to a temperature of about 50-70 degrees Celsius to be soft enough for mixing in. Melting a piece of butter is not that easy. I have tried the following ways so far:
Microwave. Put butter into a big cup and add some water (just paranoid - there's already water in butter) and turn the microwave for a minute. Works great, but butter becomes foamy and can escape the cup and dirty the oven.
Boiling water. Put butter into a big cup, add some boiling water and mix thoroughly. Works, but requires lots of effort.
Leaving on the sink and then boiling water. Put butter (still wrapped) onto the kitchen sink and leave it there for several hours so that it reaches room temperature, then use "boiling water" way. Works and is almost effortless, but requires preparation in advance.
I asked other people - the only way they suggest is water bath which is IMO too much of a hassle. I'd prefer some easy and reliable way that doesn't require lots of utensils and equipment and would be fast - so that a piece of butter out of fridge or freezer could be melted in minutes.
What convenient ways of melting butter are there?